1. Field of the Invention
The present invention relates to a digital camera employing a solid-state image sensor, forming picture image of an object, and recording onto a recording medium, in particular, to a digital camera detecting focusing condition, light metering, and performing white balance process of an object using a single solid-state image sensor, and forming picture image of the object automatically controlling itself based on measured data.
2. Description of Related Art
In order to form picture image of an object, it is necessary to know a distance to the object, light metering of the object, and white balance of the object. Accordingly, other than image sensor for forming picture image, it has been necessary to have exclusive devices for detecting such as AF (autofocus: detecting focus of the object and automatically driving the picture image forming lens based on the detected data), AE (automatic exposure: light metering of the object and controlling exposure condition (shutter speed and f-number) based on the measured data), and WB (white balance: measuring the color temperature of the object and processing appropriate color reproduction of the object based on the measured data, or AWB (automatic white balance: when this process is controlled automatically)), and, moreover, it has been necessary for each process to have exclusive optical systems according to circumstances.
For example, in AF, it has been necessary to have an exclusive optical system for arranging an AF sensor in a position equivalent to the film plane, and, furthermore, in order to calculate AF with optimum quantity of light, it has been necessary to have another sensor for monitoring incident quantity of light other than image sensor for forming picture image.
In AE, as same as AF, in order to enhance accuracy of light metering, it has been necessary to have exclusive optical system and exclusive sensor having a plurality of sensing area.
After releasing the shutter, a digital camera, other than ordinary video camera, is necessary to acquire information of the object with optimum quantity of light as fast as possible, in order to avoid losing a shutter chance. Therefore, it has been necessary to have an exclusive WB sensor for measuring color temperature of the object before forming picture image in order to record a picture with optimum WB condition.
By the way, it has variously been proposed that all or a portion of AF, AE, and AWB are performed by an image sensor. The Japanese Laid-Open Patent Application No. 2-210974 discloses an idea that an image sensor performs all of these processes.
It discloses that a CCD image sensor performs in order from AWB, AF, AE, and, then, forming picture image of an object. An outline of the contents is described below. At first, in order to perform various calculations accurately within dynamic range of the CCD, an overflow time of the CCD at brightness of the object while forming picture image is measured. In the measurement of color temperature later on, a diffusing plate is inserted in the optical system, quantity of light in the image plane is equalized, and, then, exposed. Then, output signal from the image sensor is passed through a color-separation circuit and an integrator, A/D converted, and performed AWB calculation in a CPU.
In the AF calculation after that, a defocusing lens and a phase difference detection optics are inserted into the optical system, and the CCD is exposed with aforementioned overflow time after being reset. Among the output of CCD, the only output from the AF area is selected by a switch located outside, A/D converted, and performed AF calculation in the CPU. The principle and a way to realize the AF method using phase difference is disclosed, for example, in the Japanese Laid-Open Patent Application No. 9-184973 showing a method using time sequential pupil division.
FIG. 6 shows the principle disclosed in the application. In FIG. 6, reference number 501 denotes a picture image forming lens, 502 denotes a position of an aperture stop of the picture image forming lens 501, 503 denotes a focusing plane, 502a and 502b denote two apertures located the position of the aperture stop, 505a and 505b denote light rays passing through the apertures 502a and 502b respectively, and are coincide with each other in the focusing plane 503. However, the rays are not coincide in the position 503a, and differs in connection with the separation of the apertures and the difference to the focusing plane 503.
Suppose the position of the image plane be 503a, the distance between the apertures be X, the separation of the images focused in the image plane be Y, the distance between the position of the aperture stop and the image plane be L, and the defocusing amount be Z, the following equation is satisfied;X/Y=(L−Z)/Z. 
The optical system can be focused by controlling the defocusing amount Z.
FIG. 7 is another example according to this principle disclosed in the Japanese Laid-Open Patent Application No. 9-184973. In FIG. 7, reference number 602 denotes aperture stops blocking light flux to the optical system, 604 denotes a blade arranged on the shield 602 blocking either one of double apertures, 602a or 602b. By blocking the apertures 602a and 602b by using the blade 604 in turn, time sequential signals of detected focus are output from the image sensor. The defocusing amount is calculated based on the signals, so that the optical system is controlled.
Then, in AE calculation after that, the optics used for aforementioned AF measurement is removed, and the CCD is exposed. Among the output of the CCD, either of output area according to a spot measurement or an average measurement is selected by a switch located outside, the output is integrated, A/D converted, and processed AE calculation in the CPU.
By the way, it has been proposed that the image sensor is fabricated by using CMOS process capable of realizing low cost and low power consumption. Various types of CMOS image sensor having such functions of signal processing or calculation inside the device itself have been proposed. Products applied to low priced digital camera have recently been announced.
CMOS image sensor is characterized by reading out after amplifying minute signal photoelectrically converted by photodiode by means of cell amplifier formed in each pixel. Various types of CMOS image sensor have been proposed such as SIT (Static Induction Transistor), CMD (Charge Modulation Device), BASIS (BAse Stored Image Sensor), FGA (Float Gate Array), BCMD (Bulk Charge Modulation Device), AMI (Amplified MOS intelligent Imager), and BCAST (Buried Charge Accumulator and Sensing Transistor array).
In addition to this, a vision chip integrating image sensor with calculator having a function of parallel processing for 3D image and an artificial retina chip capable of performing simple retina function have recently been announced. Regarding the artificial retina chip, application to a field such as game, cellular phone, or security system has been announced.
Principle and function of the artificial retina chip are precisely disclosed in U.S. Pat. Nos. 5,694,495 and 5,815,608. Major functions realized by the artificial retina chip are described bellow. At first, it is possible to read out lines between any two lines by sending signals to a plurality of scanners controlling readout of each column of the image sensor (sensor). Multiplication and addition of voltage supplied to the plurality of scanners and intensity of input image are obtained as output of the sensor. As a result, it is easy to obtain image output performed inter-pixel operation (emphasized profile, and the like).
Furthermore, pattern matching is made possible by sequentially supplying scanner-controlling signal as predetermined pattern to the plurality of scanners. Moreover, any range along column direction can be readout by equipping a random scanner for controlling column direction of the sensor. As a result, a picture image of any area can be read out together with the function of aforementioned any-line-readout. On occasion of a plurality of watching patterns, it is possible to read out the plurality of areas by setting a plurality of read out areas, and read out the plurality of areas in turn.
By arranging a circuit for setting a readout time to obtain the partial image after reset the censor cell according to the brightness of the part, the accumulation time can be varied by each cell or by each area. By reading out after transferred more than two lines while reading out, the resolution can be lowered, so that pattern matching can be performed much faster. Since above-mentioned various functions can be realized by single sensor, outside circuits for realizing these functions, which have been needed so far, become unnecessary, so that circuit becomes smaller and power consumption can remarkably be reduced.
Furthermore, since CCD typed image sensor usually outputs signals by transferring electric charge stored in the photoelectric converting portion in response to light exposure, once the signal is read out, no signal charge is left in the detector cell (so-called “destructive device”). On the other hand, most of the CMOS typed sensors amplify electric charge stored in the photoelectric converting portion by means of the aforementioned cell amplifier using MOS typed FET or the like and output signals converting into voltage, so that no signal charge is consumed while reading out. There is a merit to be able to read out repeatedly while detecting light (so-called “non-destructive device”).
However, when AE, AF, and AWB are processed by a single image sensor, special optical system for each measurement is needed to be arranged before each measurement. Moreover, in the aforementioned method using time sequential pupil division, since an object must be formed picture image at least twice by changing the position of the blade, it takes time and time difference occurs between the two picture images, so that focus detection for fast moving object becomes incorrect. Furthermore, the two pupils must be shielded in turn at high speed, so that the mechanism and controller become complicated, and, as a result, reliability of the mechanism is difficult to be maintained. Therefore, when a photographer releases a shutter for forming picture image of an object, it may take considerably long time to start recording the object, and, as a result, the right instant for forming picture image may be lost.